Lung macrophages may be important in pulmonary respones to inhaled antigen or in the pathogenesis of certain lung diseases. It is our hypothesis that lung macrophage populations are made up of multiple macrophage subpopulations with different immunologic functions, and that investigation of these functional subpopulations in vitro will improve our understanding of lung macrphage function in vivo. The present proposal is designed to test this hypothesis regarding lung macrophage functional heterogeneity in the rat. Rat alveolar macrophages will be obtained by lung lavage and fractionated into viable subpopulations by centrifugation through discontinuous density gradients of bovine serum albumin. Each subpopulation will then be studied for enzyme markers of cell maturation and cell activation. The subpopulations will then be assayed for the following parameters of immunologic function: a. alveolar macrophage support of mitogen-induced lymphocyte proliferation. b. alveolar macrophage support of antigen-induced lymphocyte proliferation. c. alveolar macrophage surface expression of Ia determinants. d. alveolar macrophage production of the monokine, Interleukin 1. e. alveolar macrophage tumor cell cytotoxic function. The characteristics of each alveolar macrophage subpopulation will be compared to simulatenously studied unfractionated lavged alveolar macrophages to demonstrate the contribution each macrophage subpopulation makes to the immunologic function of lavaged alveolar macrophages as a whole. Experiments outlined for the 02 year will investigate functional heterogeneity of alveolar macrophages in two animal models of pulmonary inflammation. Experiments outlined for the 03 year will study alveolar macrophages left behind after lavage and pulmonary interstitial macrophages. These studies will determine whether functional heterogeneity is a feature of alveolar macrophage populations and will contribute to the study of lavaged cells from patients with pulmonary disease.